The present invention relates to an electrophotosensitive material which is used for image forming apparatuses such as copying apparatus, etc.
In the image forming apparatuses such as copying apparatus, etc., an organic photoconductor (OPC) having a sensitivity within the wavelength range of a light source of the apparatus has exclusively been used.
As the organic photoconductor, there have been known a single-layer type electrophotosensitive material having a single photosensitive layer wherein an electric charge generating material and an electric charge transferring material are dispersed in a membrane of a suitable binding resin, and a multi-layer type electrophotosensitive material comprising an electric charge generating layer containing an electric charge generating material and an electric charge transferring layer wherein an electric charge transferring material is dispersed in a membrane of a binding resin, both layers being mutually laminated.
Examples of the electric charge generating material include phthalocyanine pigments, bisazo pigments, perylene pigments, etc.
Furthermore, examples of the electric charge transferring material include various hole transferring materials such as carbazole compounds, carbazole-hydrazone compounds, oxadiazole compounds, pyrazoline compounds, hydrazone compounds, stilbene compounds, phenylenediamine compounds, benzidine compounds, etc.
Furthermore, as the binding resin, a bisphenol A type polycarbonate having an excellent mechanical strength has hitherto been used. However, the bisphenol A type polycarbonate is liable to cause gelation because of its high crystallizability and is also insufficient in mechanical strength.
Therefore, there has recently been suggested various polycarbonates, e.g. bisphenol C type polycarbonate, bisphenol Z type polycarbonate, bisphenol Z type polycarbonate having a substituent, etc., which are superior to the bisphenol A type polycarbonate in mechanical strength, bisphenol C-copolymer type polycarbonate, etc. as the binding resin of the photoconductor (e.g. Japanese Unexamined Patent Publication Nos. 53-148263 and 1-273046).
However, when these novel polycarbonates are used for the formulation of a conventional photoconductor as they are, the mechanical strength of the photoconductor is improved but the sensitivity is deteriorated. In addition, the above photoconductor also has a problem that the sensitivity is considerably deteriorated when the image is formed repeatedly formed and so-called repeat characteristics are inferior. Furthermore, when the above novel polycarbonates are used, the mechanical strength of the photoconductor is improved but the degree of the improvement is insufficient. Such a photoconductor is also insufficient in durability and heat resistance because of its low glass transition temperature